Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$118.44	11.353%	$131.8865	$131.89	$131.90	$131.90
Purchase #2	$62.45	6.696%	$66.6317	$66.63	$66.65	$66.60
Purchase #3	$244.63	4.203%	$254.9118	$254.91	$254.90	$254.90
Purchase #4	$230.73	6.748%	$246.2997	$246.30	$246.30	$246.30
Purchase #5	$20.89	8.834%	$22.7354	$22.74	$22.75	$22.70
Purchase #6	$86.43	11.674%	$96.5198	$96.52	$96.50	$96.50
Purchase #7	$84.76	6.860%	$90.5745	$90.57	$90.55	$90.60
7 purchase totals =	$848.33		$909.5594	$909.56	$909.55	$909.50